Different location technologies are available for finding persons with mobile terminal devices. The most widely known system for outdoor localization or navigation, respectively, is the satellite-aided Global Positioning System (GPS). For localization or navigation within buildings or indoors, respectively, different approaches are known, like, for example, infrared systems, RFID systems or also field strength evaluations by IEEE 802.11 WLAN networks (WLAN=wireless local area network). The GPS system is currently only reliably available for outdoors. New developments, like highly sensitive receivers or the so-called A-GPS (assisted GPS) represent attempts to make the technology usable within buildings as well. A-GPS combines the use of the satellite-based GPS system with the reception of so-called assistance information from cellular mobile radio networks. Currently, these technologies do not yet have the desired average accuracies. Generally, infrared systems and RFID systems are not available everywhere and are tied to specific preconditions.
Due to the increasing distribution of wireless radio networks, which are, for example, based on the WLAN standard, these wireless networks are ideal as a basis for new localization methods.
Conventional localization methods used hitherto are, for example, based on triangulation, neighborhood relationships, lateration via time measurement or lateration via field strength assessment. These methods are localization methods where either a position of stationary transmitters or base stations has to be known or where training has to be performed in advance at typical positions in an environment to be covered by the localization method.
Guiding a user to a destination by means of a mobile device is generally achieved by determining the position of the mobile device and the destination. Subsequently, a path to be walked or driven along may be calculated from the relation of these two pieces of information.
If, for example, persons with mobile terminal devices or also self-sufficient systems, like, for example, automotive vehicles or robots, are in a strange environment and want to find other persons, defined places or objects or to be guided to the same, or, for example, be guided back to a starting point without complicated explanations of the way, and if the respective current positions of the persons and objects as well as a map of the environment are either not known or available, respectively, the above-described conventional localization or navigation methods will fail.